J N E R JOURNAL OF NEUROENGINEERINGAND REHABILITATION

Pieber et al. Journal of NeuroEngineering and Rehabilitation (2015) 12:51 DOI 10.1186/s12984-015-0046-0

RESEARCH Open Access

Optimizing stimulation parameters infunctional electrical stimulation ofdenervated muscles: a cross-sectional study

Karin Pieber1, Malvina Herceg1, Tatjana Paternostro-Sluga2 and Othmar Schuhfried1*

Abstract

Background: To counteract denervation atrophy long-term electrical stimulation with a high number of musclecontractions has to be applied. This may lead to discomfort of the patient and negative side effects like burns. Afunctional effective muscle contraction induced by the lowest possible stimulation intensity is desirable. In clinicalpractice a selective stimulation of denervated muscles with triangular pulses is used.The aim of the study was to evaluate the influence of polarity and pulse duration on the stimulation intensity oftriangular pulses in denervated muscles in patients with peripheral nerve lesions.

Methods: Twenty-four patients with denervated extensor digitorum communis muscle and twenty-four patientswith denervated tibialis anterior muscle due to peripheral nerve lesions were included. Four different combinationsof triangular pulses with various duration and polarity were delivered randomly to the denervated muscles. Thethreshold intensity to induce a functional effective muscle contraction was noted. One-way within subject ANOVAwas used to assess changes in intensity. An alpha level of p less than or equal to 0.05 was the criterion for statisticalsignificance.

Results: Patients with a denervated tibialis anterior muscle presented significant lower intensities inducing afunctional effective muscle contraction in favor of the stimulation with a duration of 200 ms and a polarity with thecathode proximally applied. No significant differences could be shown between the different stimulation protocolsin case of denervated extensor digitorum communis muscle.

Conclusions: We recommend electrical stimulation of the denervated tibialis anterior muscle with triangularcurrent with a duration of 200 ms and a polarity with the cathode proximally applied.

Keywords: Electrical stimulation, Denervation, Chronaxie, Polarity, Pulse duration

BackgroundDenervation of muscles leads to loss of voluntary and reflexactivity, muscle atrophy and changes in muscle excitability[1]. Denervated muscles are different from innervatedmuscles in their response to electrical stimulations. A dir-ect stimulation of the muscle fiber with a greater electriccharge is needed [2]. To selectively stimulate a denervatedmuscle, a slow rising triangular pulse is required as thismuscle has less ability to accommodate [2]. This selectivestimulation is necessary to avoid the overstimulation of

* Correspondence: othmar.schuhfried@meduniwien.ac.at1Department of Physical Medicine and Rehabilitation, Medical University ofVienna, General Hospital of Vienna, Waehringer Guertel 18-20, 1090 Vienna,AustriaFull list of author information is available at the end of the article

© 2015 Pieber et al. This is an Open Access ar(http://creativecommons.org/licenses/by/4.0),provided the original work is properly creditedcreativecommons.org/publicdomain/zero/1.0/

the innervated muscles in the surroundings and to avoidthe stimulation of sensory fibers [3]. The long rise timeand the long pulse duration is suitable to stimulate dener-vated muscle fibers since a denervated muscle has higherchronaxie values. Chronaxie is defined as the duration (inms) of a rectangular pulse with the two-fold intensity ofthe rheobase which just reaches the stimulation thresholdat which a muscle twitch occurs. Chronaxie values above1 ms are described as a sign of muscle denervation [4, 5].To cause a contraction in denervated muscles either rect-angular pulses of sufficient duration (30 ms or more) ortriangular pulses of long duration (100–500 ms) can beused [2]. But the use of rectangular pulses can result in ex-cessive recruitment of neighboring innervated muscles

ticle distributed under the terms of the Creative Commons Attribution Licensewhich permits unrestricted use, distribution, and reproduction in any medium,. The Creative Commons Public Domain Dedication waiver (http://) applies to the data made available in this article, unless otherwise stated.

Table 1 Characteristics of the study population

Extensor digitorumcommunis muscle (n = 24)

Tibialis anteriormuscle (n = 24)

Age (years) 47.2 ± 18.4 (19–78) 51.9 ± 18 (23–81)

Duration of lesion(weeks)

14.5 ± 21.1 (2–100) 13.2 ± 14.1 (2–50)

Strength (MRC scale) 1.0 ± 0.9 (0–3.5) 2.2 ± 1.4 (0–4)

Chronaxie (ms) 16.9 ± 18.9 (0.4–80) 16.2 ± 9.5 (0.7–35)

Data in mean ± SD (range), ms milliseconds

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and can be limited due to patient’s sensation due to stimu-lation of sensory fibers [3, 6]. In clinical practice, mainlytriangular pulses with a pulse duration of 200 ms or500 ms are used. By the use of more than 100 ms pulseduration, the strength-duration curves (also known asintensity/time curve - I/t-curve) for triangular pulses dif-fers between denervated and innervated muscles with ahigher threshold for innervated muscle. Therefore, the se-lective stimulation of the denervated muscle is possible [3,7]. The threshold current intensity might be significantlylower when stimulating with 500 ms rather than 200 ms.Because of the positively charged outer surface of thenerve membrane the negatively charged electrode (cath-ode) is more effective in stimulating excitable tissue thanthe positively charged electrode (anode) [1, 2]. Therefore,a change of polarity might require a different currentintensity to stimulate a muscle. Overall, the stimulationshould achieve a moderately strong contraction withoutunnecessary discomfort for the patient [3] and resemble anormal activity of the motor neuron [8].Functional electrical stimulation (ES) is one treatment op-

tion for denervated muscles to preserve or restore musclestrength and reduce or prevent muscle atrophy due to de-nervation and disuse [1, 2]. To our knowledge, only fewhuman studies are dealing with this topic [9–13]. Thesestudies included patients suffering from spinal cord injur-ies [9, 11, 13], lumbosacral plexus avulsion trauma with alower extremity monoparesis [10] or total peripheral nervelesions of the median, ulnar or peroneal nerve [12]. Theyused rectangular pulses with long duration [9, 11–13].One study used transcutaneous electrical muscle stimula-tion without information concerning the stimulation pa-rameters [10]. Most of these studies were not recentlypublished [6, 9–12] and were no RCTs [6, 9–11, 13],but case based pilot or longitudinal studies with a smallsample size. Only Boonstra et al. [12] used a randomized-controlled design. But the author had to mention thesometimes bad motivation of the patients and thereforenot optimal performance of the ES which may have nega-tive impact on the results. The effects of ES in denervatedmuscles have been discussed controversially concerningmaintaining muscle mass until re-innervation and possibledelay in neuromuscular recovery [14, 15].To the best of our knowledge, no human study has

evaluated ES with triangular pulses in denervated muscles.Animal experiments with triangular pulses have shown adecreased expression of atrophy genes, but ES did notavert the loss of muscle mass due to denervation [16, 17].This may be explained by the low number of muscle con-tractions triggered by ES [18].In ES of denervated human and animal muscles triangu-

lar and rectangular pulses have not been compared yet.Nevertheless, this is an important topic in rehabilitation ofperipheral nerve lesions as functional ES with triangular

pulses is broadly and successfully used in clinical practicealthough recommendations are mostly based on clinicalbooks and empirical [1, 2].No study has evaluated in detail the effect of pulse

duration and polarity of triangular pulses in the stimula-tion of human denervated muscle. Thus, the aim of thisstudy was to evaluate the impact of stimulation parame-ters such as polarity and pulse duration during func-tional ES with triangular pulses of denervated muscles inthe upper and lower extremity in patients with periph-eral nerve lesions on required intensity for an effectivemuscle contraction.

MethodsParticipantsTwenty-four patients (9 female/15 male) with dener-vated extensor digitorum communis muscle (EDC) andtwenty-four patients (8 female/16 male) with denervatedtibialis anterior muscle (TA) were included in this study.Characteristics of included patients are presented inTable 1.

SetupAll examinations were conducted in the electrophysio-logical laboratory of the Department of Physical Medicineand Rehabilitation of the Medical University of Vienna.Two senior physicians, experienced in nerve conductionvelocity studies (NCV), evaluations of chronaxie and func-tional ES, performed the examinations. The cross-sectionaltesting were carried out during daily routine of an out-patient department. Patients with a denervated EDC dueto a lesion of the radial nerve, plexopathy or radiculopathyor denervated TA due to a lesion of the peroneal nerve,plexopathy or radiculopathy referred to electrophysio-logical examination and evaluation for long-term ES wereincluded consecutively in this study. Patients with severeimpairments of cognition and communication, epilepsy,cardiac pacemakers, edema, skin lesions and younger than19 years were excluded. The testing was not wearing, thestudy protocol was approved by the head office of theDepartment and performed according to the guidelinesof good clinical practice, following the principles of theDeclaration of Helsinki.

Pieber et al. Journal of NeuroEngineering and Rehabilitation (2015) 12:51 Page 3 of 7

Procedure (see Fig. 1)The peripheral nerve lesion was confirmed by NCV orby evaluating chronaxie values. The time from the onsetof the lesion was recorded in weeks. Prior to electro-physiological testing the strength of the EDC and TAwas assessed using the Medical Research Council Scale(MRC Scale) which uses the numeral grades 0–5 (0 – nomovement, 1 – a flicker of movement is seen or felt inthe muscle, 2 – muscle moves the joint when gravity iseliminated, 3 – muscle cannot hold the joint against resist-ance, but moves the joint fully against gravity, 4 – muscleholds the joint against a combination of gravity and mod-erate resistance, 5 – normal strength) [19, 20]. Electro-physiological examination for determination of chronaxiewas performed with a constant-current electrical stimula-tor (Endomed 982, Enraf-Nonius, Netherlands) as de-scribed by Paternostro-Sluga et al. [5] and NCV with anelectro-diagnostic machine (Keypoint; Medtronic, DantecMedical A/S, Skovlunde, Denmark).Functional ES was applied with the constant-current

electrical stimulator mentioned above. In bipolar arrange-ment, two 30 mm diameter adhesive electrodes (Stimcom®,

Fig. 1 Procedure of testing and stimulation protocol

Comepa, France) were used for the stimulation of theEDC (see Fig. 2) and two 50×50 mm adhesive electrodes(Stimcom®, Comepa, France) for the stimulation of the TA(see Fig. 3). Electrodes (anode and cathode) were placedover the muscle in its longitudinal plane, with one elec-trode at the proximal end of the muscle belly and theother electrode at the distal end of the muscle belly. Thedistance was adapted based on the length of the muscle.For this short evaluation surface electrodes were used asthey are convenient and used in therapy. Monophasic tri-angular pulses were delivered to the denervated muscle todetermine the threshold intensity (in mA) in order to elicita clearly visible muscle contraction and joint movementwhile not causing the patient unnecessary discomfort.Stimulation of the TA induced foot dorsiflexion, stimula-tion of the EDC induced finger extension. We havechosen this definition of “effective muscle contraction” asit is also used in clinical practice when receiving this treat-ment. The current intensity was increased stepwise with0.1 mA per second. Testing was performed with a fre-quency of 1 Hz in a standardized position, with a supineposition for testing the TA and sitting for the EDC. Each

Fig. 2 Stimulation of the extensor digitorum communis muscle (EDC). Positioning of electrodes in bipolar arrangement with two 30 mmdiameter adhesive electrodes were used for the stimulation of the EDC. Electrodes (anode and cathode) were placed over the muscle in itslongitudinal plane, with one electrode at the proximal end of the muscle belly and the other electrode at the distal end of the muscle belly

Pieber et al. Journal of NeuroEngineering and Rehabilitation (2015) 12:51 Page 4 of 7

trial for testing a combination of stimulation parameterslasted between 1 and 2 min (depending on the thresholdintensity). The duration of recovery was twice the dur-ation of one trial.Intensity was recorded in absolute values (INT) in mA

and relatively (REL) provided in percentage to the firststimulation of each patient. Due to individual differencesin degree of muscle atrophy (possibly more pronounced inchronic denervation), differences in limb circumference,amount of subcutaneous fat tissue, and different skin con-ductance the needed absolute current intensities can vary.These individual differences can be balanced by assessingthe relative measure of the applied current intensity.Four different combinations of pulse duration and po-

larity were evaluated: 1) duration of 200 ms; anode prox-imal and cathode distal (E 200+), 2) duration of 200 ms;

Fig. 3 Stimulation of the tibialis anterior muscle (TA). Positioning of electrowere used for the stimulation of the TA. Electrodes (anode and cathode) welectrode at the proximal end of the muscle belly and the other electrode

cathode proximal and anode distal (E 200-), 3) durationof 500 ms; anode proximal and cathode distal (E 500+)and 4) duration of 500 ms; cathode proximal and anodedistal (E 500-). The sequel of ES with the different com-binations of pulse duration and polarity was randomlyassigned by a randomization list. The investigator whonoted the muscle contraction was blinded to the appliedintensity and stimulation parameters.

StatisticsData were analyzed using the Statistical Package for SocialSciences (SPSS) Version 15.0. Data of patients with dener-vated TA and denervated EDC were analyzed separately.After a check of the data’s normal distribution (testing forkurtosis and skewness, one-sample Kolmogorov-Smirnovtest, p ≤ 0.05), a one-way within subject ANOVA was used

des in bipolar arrangement with two 50×50 mm adhesive electrodesere placed over the muscle in its longitudinal plane, with oneat the distal end of the muscle belly

Table 3 One-way within subject ANOVA of patients withdenervated EDC muscle

df F Level of significance

INT (mA) 2.4 0.97 0.4

REL (%) 2.3 0.99 0.4

INT intensity recorded in absolute values in mA, REL intensity relatively providedin percentage to the first stimulation of each patient, EDC extensor digitorumcommunis, df degrees of freedom, F F-ratio, level of significance (p-value) of thetwo variables

Pieber et al. Journal of NeuroEngineering and Rehabilitation (2015) 12:51 Page 5 of 7

to assess changes in INT and REL. We calculated thesphericity of the variables with the Mauchly’s test. If thecondition of sphericity was not met, the inner-subject ef-fects were tested with the Huynh-Feldt test. An alpha levelof p ≤ 0.05 was the criterion for statistical significance. Incase of statistical significance in ANOVA, planned con-trast were used to test specific hypotheses on the differ-ences between the means of the various groups.

ResultsDenervated EDCThe Kolmogorov-Smirnov test resulted in a normal datadistribution of INT and REL. Table 2 shows the descriptivedata of the four different combinations of pulse durationand polarity for patients with denervated EDC. TheMauchly’s test indicated that the assumption of sphericitywas violated for the main effects of INT (χ2 (5) = 25.694,p < 0.001) and REL (χ2 (5) = 22.205, p < 0.001). Therefore,we used the Huynh-Feldt test for sphericity correction toproduce more accurate significant values. ANOVA did notshow a significant difference between the four combina-tions for the two variables (Table 3).

Denervated TAThe Kolmogorov-Smirnov test resulted in a normal datadistribution of INT and REL. Table 4 shows the descriptivedata of the four different combinations of pulse durationand polarity for patients with denervated TA. Mauchly’stest indicated that the assumption of sphericity was vio-lated for the main effects of INT (χ2 (5) = 22.765, p <0.001) and REL (χ2 (5) = 37.108, p < 0.001). Therefore, weused the Huynh-Feldt test for sphericity correction to pro-duce more accurate significant values. ANOVA evaluateda significant difference between groups for REL, and forINT a tendency to significance (see Table 5). Contrasts re-vealed lower values for REL, thus E 200- differs signifi-cantly from E 200+, E 500+ and E 500- (F (1,23) = 8.367,p = 0.008) (see Table 4).

DiscussionPatients with denervated TA presented significant differ-ences in the variable REL. E 200- needed significantly lessrelative intensity to obtain a good visible and functional

Table 2 Descriptive data of the different pulse combinations forpatients with denervated EDC muscle

INT (mA) REL (%)

E 200+ 5.4 ± 2.3 105.2 ± 20.5

E 200− 5.3 ± 2.5 103.5 ± 31.7

E 500+ 5.0 ± 2.4 96.0 ± 21.9

E 500− 5.6 ± 3.0 104.3 ± 29.0

Data in mean ± SD (range), INT intensity recorded in absolute values in mA,REL intensity relatively provided in percentage to the first stimulation of eachpatient, EDC extensor digitorum communis

effective muscle contraction. In case of denervated EDC,the outcome variables INT and REL showed no significantdifferences between the different groups.We used bipolar electrode placement as it is known

to obtain higher-magnitude evoked contractions [1] andstimulates the whole muscle. The current is applied in thelong axis of the muscle fibers, stimulating at each end ofthe muscle belly [2]. Furthermore, it is the most suitableelectrode configuration in clinical practice. In the TA, therelevance of the polarity might be due to the intrinsicproperties of the muscle, such as the individual pattern ofmotor nerve branching [21, 22], and the anatomy of theendplate zones. The TA is innervated by 2 to 4 motornerve branches of the deep peroneal nerve [23]. It wasdiscussed that individual motor nerve branching mightinfluence the muscle’s response to ES [24]. Bowden et al.identified the area of the lowest electrical threshold andmaximum muscle response to ES in human TA in theproximal part of the muscle [25]. The negatively chargedelectrode (cathode) is usually more effective in activatingexcitable tissue than the positively charged electrode(anode) [1, 2]. This may explain why a significantly lowerintensity is needed when the cathode is placed at the prox-imal part of the muscle (E 200-). In contrast to the TA,the motor points are located in the middle third of themuscle in the EDC [26].A key factor for preservation of muscle mass and func-

tion is the number of induced contractions [18, 27]. There-fore, a highly intensive stimulation protocol with long-termES and a high number of muscle contractions is recom-mended [9, 11, 13]. The minimization of the amount ofcurrent applied while inducing a visible and valid musclecontraction has a high impact on acceptance by patients

Table 4 Descriptive data of the different pulse combinations forpatients with denervated TA muscle

INT (mA) REL (%)

E 200+ 8.9 ± 3.8 123.0 ± 36.1

E 200− 7.4 ± 4.2 97.6 ± 26.5

E 500+ 8.5 ± 3.1 118.3 ± 35.0

E 500− 8.1 ± 4.3 108.5 ± 35.2

Data presented in mean ± SD (range), INT intensity recorded in absolute valuesin mA, REL intensity relatively provided in percentage to the first stimulationof each patient, TA tibialis anterior

Table 5 One-way within subject ANOVA of patients withdenervated TA muscle

df F Level of significance

INT (mA) 1.4 3.1 0.073

REL (%) 1.7 4.7 0.02

INT intensity recorded in absolute values in mA, REL intensity relativelyprovided in percentage to the first stimulation of each patient, TA tibialisanterior, df degrees of freedom, F F-ratio, level of significance (p-value) of thetwo variables

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performing ES, especially over a longer time period. Theminimizing of current intensity could reduce the sensationof discomfort, which may be the major limitation of ES[21]. Furthermore, for long time use a current of low in-tensity is requested in light of possible skin irritation aswell as electrochemical burns. These are caused by pHchanges at the electrode-tissue interface and appear if thestimulation is prolonged or with a high current density[28]. In preventing electrochemical injuries one of themost important factors beside the proper electrode type isminimizing and maintaining the current intensity as lowas possible but still inducing a muscle contraction [29]. Inthis study, an extension of the pulse duration from 200 msto 500 ms did not result in a decrease in intensity (seeTable 4). Therefore, the use of 200 ms rather than 500 msis preferable, since a longer pulse duration increases therisk of skin irritation by increasing the total amount ofcurrent flow. In contrast to rectangular pulses, the tri-angular pulse allows a selective stimulation of the dener-vated muscles without stimulation of the neighboringinnervated muscles.We chose the above mentioned peripheral nerve le-

sions as they are the most frequently transferred to ourlaboratory which are usually treated with ES. The radialnerve is indicated as the most frequently injured periph-eral nerve in the upper extremity [30, 31] and frequentlyinjured secondary to fractures [32]. The peroneal nerveis known to be the most sensitive peripheral nerve in thelower extremity to lesions due to poor vascularization anda superficial position [33]. Mostly stretch, contusions, lac-erations, tumors, entrapments or compressions are thecauses for this lesion [34]. Because the TA is the mainmuscle responsible for ankle dorsiflexion it is often elec-trically stimulated to prevent drop foot and therefore toimprove locomotion efficiency. We do not think that ourresults can be generalised to other patient populationsand muscle groups. Perhaps a longer duration after the in-jury or a greater denervation will have an impact on thereaction to ES. Therefore, we used REL because in pa-tients with more chronic and more pronounced nerve le-sions absolute current intensities might differ due to thegreater muscle atrophy.The visual assessment of the effective muscle contrac-

tion might be seen as limitation. The small sample size

and cross-sectional design are further limitations in thisstudy.

ConclusionsBased on our results, we recommend ES of the dener-vated TA with triangular current pulses with a durationof 200 ms and a polarity with the cathode applied proxim-ally. In case of denervated EDC, polarity and pulse durationseem to be without impact. With these optimized stimula-tion parameters the effect of ES with triangular pulses inperipheral nerve lesions has to be evaluated in humanfollow-up studies in comparison to rectangular pulses.

AbbreviationsES: Electrical stimulation; EDC: Extensor digitorum communis muscle;TA: Tibialiss anterior muscle.

Competing interestsThe authors declare that they have no competing interests.

Authors’ contributionsKP and OS conducted the examinations. KP and MH drafted the manuscript.TP-S and OS participated in the study design and conception and interpretationof data. All authors read and approved the final manuscript.

AcknowledgmentsWe thank Dr. Rudolf Debelak for the statistical analysis of the data.

Author details1Department of Physical Medicine and Rehabilitation, Medical University ofVienna, General Hospital of Vienna, Waehringer Guertel 18-20, 1090 Vienna,Austria. 2Institute of Physical Medicine and Rehabilitation, Donauspital,Vienna, Austria.

Received: 19 February 2015 Accepted: 2 June 2015

References1. Robinson AJ. Physiology of muscle and nerve. In: Robinson AJ, Snyder-Mackler L,

editors. Clinical electrophysiology: electrotherapy and electrophysiologictesting. Baltimore: Lippincott Williams & Wilkins; 2008. p. 71–105.

2. Low J, Reed A. Electrical stimulation of nerve and muscle. In: Low J, Reed A,editors. Electrotherapy explained: principles and practice. Oxford, UK:Butterworth-Heinemann; 2000. p. 53–140.

3. Cummings JP. Conservative management of peripheral nerve injuriesutilizing selective electrical stimulation of denervated muscle withexponentially progressive current forms. J Orthop Sports Phys Ther.1985;7(1):11–5.

4. Harris R. Chronaxy. In: Licht S, editor. Electrodiagnosis andelectromyography. Baltimore: Waverly Press; 1971. p. 218–39.

5. Paternostro-Sluga T, Schuhfried O, Vacariu G, Lang T, Fialka-Moser V.Chronaxie and accommodation index in the diagnosis of muscle denervation.Am J Phys Med Rehabil. 2002;81(4):253–60.

6. Woodcock AH, Taylor PN, Ewins DJ. Long pulse biphasic electricalstimulation of denervated muscle. Artif Organs. 1999;23(5):457–9.

7. Wynn Parry, C. Strength-duration curves. Electrodiagnosis andElectromyography. 3rd ed. New Haven: E. Licht; 1971. p. 241-71.

8. Eberstein A, Eberstein S. Electrical stimulation of denervated muscle: is itworthwhile? Med Sci Sports Exerc. 1996;28(12):1463–9.

9. Kern H, Salmons S, Mayr W, Rossini K, Carraro U. Recovery of long-termdenervated human muscles induced by electrical stimulation. Muscle Nerve.2005;31(1):98–101. doi:10.1002/mus.20149.

10. Cakmak A. Electrical stimulation of denervated muscles. Disabil Rehabil.2004;26(7):432–3. doi:10.1080/09638280410001663157.

11. Modlin M, Forstner C, Hofer C, Mayr W, Richter W, Carraro U, et al. Electricalstimulation of denervated muscles: first results of a clinical study. ArtifOrgans. 2005;29(3):203–6. doi:10.1111/j.1525-1594.2005.29035.x.

Pieber et al. Journal of NeuroEngineering and Rehabilitation (2015) 12:51 Page 7 of 7

12. Boonstra AM, van Weerden TW, Eisma WH, Pahlplatz VB, Oosterhuis HJ. Theeffect of low-frequency electrical stimulation on denervation atrophy inman. Scand J Rehabil Med. 1987;19(3):127–34.

13. Kern H, Carraro U, Adami N, Biral D, Hofer C, Forstner C, et al. Home-basedfunctional electrical stimulation rescues permanently denervated muscles inparaplegic patients with complete lower motor neuron lesion. NeurorehabilNeural Repair. 2010;24(8):709–21.

14. Parizotto NA. Is electrical stimulation a consolidated treatment fordenervated muscles and functional recovery after nerve injuries? MuscleNerve. 2011;43(2):299–300.

15. Salmons S. Is stimulation of denervated muscle contraindicated when thereis potential for reinnervation? Muscle Nerve. 2011;43(2):300.

16. Russo TL, Peviani SM, Freria CM, Gigo‐Benato D, Geuna S, Salvini TF.Electrical stimulation based on chronaxie reduces atrogin‐1 and myoD geneexpressions in denervated rat muscle. Muscle Nerve. 2007;35(1):87–97.

17. Russo TL, Peviani SM, Durigan JL, Gigo-Benato D, Delfino GB, Salvini TF.Stretching and electrical stimulation reduce the accumulation of MyoD,myostatin and atrogin-1 in denervated rat skeletal muscle. J Muscle Res CellMotil. 2010;31(1):45–57.

18. Dow DE, Cederna PS, Hassett CA, Kostrominova TY, Faulkner JA, Dennis RG.Number of contractions to maintain mass and force of a denervated ratmuscle. Muscle Nerve. 2004;30(1):77–86.

19. Medical Research Council. Aids to examination of the peripheral nervoussystem. Memorandum no. 45. London: Her Majesty’s Stationary Office; 1976.

20. Paternostro-Sluga T, Grim-Stieger M, Posch M, Schuhfried O, Vacariu G,Mittermaier C, et al. Reliability and validity of the Medical Research Council(MRC) scale and a modified scale for testing muscle strength in patients withradial palsy. J Rehabil Med. 2008;40(8):665–71. doi:10.2340/16501977-0235.

21. Gobbo M, Maffiuletti NA, Orizio C, Minetto MA. Muscle motor pointidentification is essential for optimizing neuromuscular electrical stimulationuse. J Neuroeng Rehabil. 2014;11:17. doi:10.1186/1743-0003-11-17.

22. Botter A, Oprandi G, Lanfranco F, Allasia S, Maffiuletti NA, Minetto MA. Atlasof the muscle motor points for the lower limb: implications for electricalstimulation procedures and electrode positioning. Eur J Appl Physiol.2011;111(10):2461–71. doi:10.1007/s00421-011-2093-y.

23. Reebye O. Anatomical and clinical study of the common fibular nerve.Part 1: anatomical study. Surg Radiol Anat. 2004;26(5):365–70.doi:10.1007/s00276-004-0238-y.

24. Maffiuletti NA. Physiological and methodological considerations for the useof neuromuscular electrical stimulation. Eur J Appl Physiol. 2010;110(2):223–34.doi:10.1007/s00421-010-1502-y.

25. Bowden JL, McNulty PA. Mapping the motor point in the human tibialisanterior muscle. Clin Neurophysiol. 2012;123(2):386–92. doi:10.1016/j.clinph.2011.06.016.

26. Walthard KM, Tchicaloff M. Motor points. Electrodiagnosis andelectromyography. 3rd ed. New Haven: E. Licht; 1971. p. 153–70.

27. Salvini TF, Durigan JL, Peviani SM, Russo TL. Effects of electrical stimulationand stretching on the adaptation of denervated skeletal muscle:implications for physical therapy. Rev Bras Fisioter. 2012;16(3):175–83.

28. Bolton L. TENS electrode irritation. J Am Acad Dermatol. 1983;8(1):134–5.29. Stecker MM, Patterson T, Netherton BL. Mechanisms of electrode induced

injury. Part 1: theory. Am J Electroneurodiagnostic Technol. 2006;46(4):315–42.30. Barton NJ. Radial nerve lesions. Hand. 1973;5(3):200–8.31. Venouziou AI, Dailiana ZH, Varitimidis SE, Hantes ME, Gougoulias NE,

Malizos KN. Radial nerve palsy associated with humeral shaft fracture. Isthe energy of trauma a prognostic factor? Injury. 2011;42(11):1289–93.doi:10.1016/j.injury.2011.01.020.

32. Mondelli M, Morana P, Ballerini M, Rossi S, Giannini F. Mononeuropathies ofthe radial nerve: clinical and neurographic findings in 91 consecutive cases.J Electromyogr Kinesiol. 2005;15(4):377–83. doi:10.1016/j.jelekin.2005.01.003.

33. Mumenthaler M, Stöhr M, Müller-Vahl H. Läsionen einzelner Nerven imBeckenbereich und an den unteren Extremitäten. In: Mumenthaler M, StöhrM, Müller-Vahl H, editors. Läsionen peripherer Nerven und radikuläresyndrome. Stuttgart: Thieme; 2003. p. 344–406.

34. Kim DH, Murovic JA, Tiel RL, Kline DG. Management and outcomes in 318operative common peroneal nerve lesions at the Louisiana State UniversityHealth Sciences Center. Neurosurgery. 2004;54(6):1421–8. discussion 8–9.

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